Systematics Section / ASPT
Davis, Jerrold I. , Soreng, Robert J. .
A phylogenetic analysis of the grass subfamily Pooideae (Poaceae), with a focus on the Poeae/Aveneae/Hainardieae complex, and the evolution of structural features of the plastid and nuclear genomes.
Phylogenetic relationships in the grass family (Poaceae) were analyzed on the basis of nucleotide sequence variation in four plastid-encoded genes (ndhF, ndhH, rbcL, and matK), with specific attention to the internal structure of subfamily Pooideae. The resulting phylogenetic hypothesis was examined with attention to the taxonomic distributions of a series of inversions and insertion/deletion characters, the absence of intron ten of the nuclear gene GBSSI (waxy), and positions of the two boundaries between the Short Single Copy (SSC) region and the neighboring Inverted Repeat (IR) regions of the plastid genome, relative to the endpoints of ndhF and ndhH, which span these boundaries in some taxa. The loss of GBSSI intron ten is interpreted as a synapomorphy of Poeae sens. lat., (i.e., including the Poeae, Aveneae, and Hainardieae, as traditionally circumscribed), and the results favor a novel set of relationships among the tribes of Pooideae, with Brachypodieae, Bromeae, Triticeae, and Poeae sens. lat. constituting a clade for which a three-nucleotide inversion in ndhF is interpreted as a synapomorphy, while a six-nucleotide inversion in ndhF marks subtribe Aveninae within Poeae sens. lat. Genera of the Poeae/Aveneae/Hainardieae complex are intermixed in a complex manner, with some of their constituent subtribes resolved as monophyletic, and others not. Neither the traditional Poeae nor the traditional Aveneae is fully nested within the other group, so the conflict between these results and traditional classifications cannot be explained simply in terms of paraphyly of one group relative to the other. Because this phylogeny is based on a set of plastid-encoded genes, it cannot by itself distinguish between reticulate evolution and parallelism in morphological characters as potential explanations for its incongruence with traditionally recognized relationships.
1 - Cornell University, L.H. Bailey Hortorium, Department of Plant Biology, Ithaca, New York, 14853, U.S.A.
2 - Smithsonian Institution, Department of Botany, MRC166, National Museum of Natural History, P.O. Box 37012, Washington, DC, 20013-7012, USA
Presentation Type: Paper
Location: Cottonwood B (Snowbird Center)
Date: Monday, August 2nd, 2004
Time: 4:00 PM